An organic electroluminescence (“electroluminescence” will be occasionally referred to as “EL”, hereinafter) device is a spontaneous light emitting device which utilizes the principle that a fluorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied. Since an organic EL device of the laminate type driven under a low electric voltage was reported by C. W. Tang et al. of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Pages 913, 1987), many studies have been conducted on organic EL devices using organic materials as the constituting materials.
Tang et al. used a laminate structure using tris(8-hydroxyquinolinol aluminum) for the light emitting layer and a triphenyldiamine derivative for the hole transporting layer. Advantages of the laminate structure are that the efficiency of hole injection into the light emitting layer can be increased, that the efficiency of forming excited particles which are formed by blocking and recombining electrons injected from the cathode can be increased, and that excited particles formed among the light emitting layer can be enclosed
As the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron transporting and light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer and an electron transporting (injecting) layer are well known.
To increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the structure of the device and the process for forming the device have been studied. As the light emitting material of the organic EL device, chelate complexes such as tris(8-quinolinolato)aluminum, coumarine derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives and oxadiazole derivatives are known. It is reported that light in the visible region ranging from blue light to red light can be obtained by using these light emitting materials, and development of a device exhibiting color images is expected (refer to, for example, Patent literatures 1, 2 and 3).
In addition, Patent literature 4 discloses a device having phenylanthracene derivatives as a light emitting material. Although the anthracene derivatives were used as a blue light emitting material, it has been required to extend a lifetime of the device. A material having naphthyl groups at 9th and 10th positions of anthracene is disclosed in Patent literature 5 and a material having fluoranthene at 9th and 10th positions for a device is disclosed in Patent literature 6.
Although these anthracene derivatives were used as a blue light emitting material, it has been required to improve a lifetime of the device.
Further, Patent literature 7 discloses various types of anthracene derivatives to be used for a hole transporting material. However, these have not yet been evaluated as a light emitting material.
[Patent literature 1] Japanese Patent Application Laid-Open No. Heisei 8(1996)-239655
[Patent literature 2] Japanese Patent Application Laid-Open No. Heisei 7(1995)-138561
[Patent literature 3] Japanese Patent Application Laid-Open No. Heisei 3(1991)-200289
[Patent literature 4] Japanese Patent Application Laid-Open No. Heisei 8(1996)-012600
[Patent literature 5] Japanese Patent Application Laid-Open No. Heisei 11(1999)-3782
[Patent literature 6] Japanese Patent Application Laid-Open No. 2001-257074
[Patent literature 7] Japanese Patent Application Laid-Open No. 2000-182776